Reduced Iron Powder Research Articles

Effect of the particle-size distribution of atomized iron powder and mixtures of atomized and reduced iron powders on some properties of materials produced from them by pressing and sintering

1. Experimental evidence clearly indicates that under conditions of identical total porosity in respective materials, the strength of compacts from atomized iron powder increases and the mechanical properties (σtr,σt, andδ) of the resultant material in the sintered condition improve with decreasing mean pore size of the material. Fine porosity achieved by pressing a mixture of specially chosen fractions is preferable to the fine porosity of a material obtained from a fine single fraction, because it ensures an optimum combination of powder compressibility and compact strength, as a result of which pressing and sintering under the same conditions enable higher density and strength and better ductility to be attained. 2. From the results of an investigation of the processing properties exhibited by mixtures of reduced and atomized iron powders (with or without 0.8% zinc stearate), it follows that the poor compactibility characteristic of atomized iron powder can be substantially improved by adding to it a suitable amount of reduced iron powder, although this measure has an adverse effect on its apparent density and compressibility. 3. At a given porosity (12%) the mechanical properties of materials produced by pressing and sintering various types of iron powder (atomized, reduced, and their mixtures) are virtually identical (σt= 20–21 kgf/mm2,δ = 13.8–14.6%), but after pressing and sintering under the same conditions better mechanical properties are obtained with atomized iron powder, which is characterized by higher compressibility.

焼結銅鋼について

The sintering process of Fe-C binary mixed powder compacts and Fe-Cu-C ternary mixed powder compacts was studied mainly from the viewpoint of phase transformation and diffusion.The results obtained were as follows:(1) After the α→γ transformation during heating in vacuum of 10-5mmHg for the Fe-C binary mixed powder compacts, the expansion was observed, the amount of which was nearly in proportion to the amount of additional graphite, and the expansion curve in dilatation and the combined carbon concentration curve well agreed. This means that the carburization was done mainly by the carbon diffusion through the contacting surface of graphite and iron powder rather than through the medium CH4 or CO gas.(2) From the vacuum measurement, it was apparent that the amount of gas discharge from the specimen with the reduced iron powder was by far larger than that from the other specimens. On the contrary, its dilatational expansion was minimum, indicating that the specimen was not swelled by the gas pressure.(3) It was clarified from the thermal analysis that the elimination of the abnormal expansion observed during sintering process of Fe-Cu binary mixed powder compacts was carried out by the liquid phase sintering related to the ternary monotecto-eutectic reaction at 1095°C.(4) The extremely rapid critical cooling rate of 1100°C/sec. was obtained from the Fe-1.0%C binary sintered compacts, while it became 360°C/sec. for the Fe-2.0%Cu-C ternary sintered compacts, and 140°C/sec. for the Fe-6.5%Cu-1.0%C ternary sintered compacts.

Correlations of Disk Compression, Ring Compression, and Bending Strengths with Uniaxial Tensile Strength of Metal Powder Compacts

Three different testing methods for measuring the tensile strength of metal powder compacts are performed and compared with the conventional uniaxial tension method. These are a test in which a disk is compressed diametrically (disk compression test), a test in which a ring is compressed diametrically (ring compression test), and a bending test. Powders used are reduced iron powders, electrolyticcopper powders, 'and atomized aluminium powders.It is shown that a correlation, may exist between uniaxial, tensile strength and, bending, strength, and in anticipation of about ±15 per cent error uniaxial tensile strength is nearly equivalent to the value that is multi-plied bending strength by 1/3. The mechanism of fracture in the disk compression varies with the kind of powder and the green density, so that the disk compression test is not suitable for a testing method to estimate uniaxial tensile strength. In the ring, compression test there is a.question how to take the stress concentration factor, and moreover, the strength varies with. the rate of inner diameter with respect to outer one even if, the green density is all the same. Therefore the ring compression test is not suitable for, it too.

Fe-C 2元系混合圧粉体の焼結について

The sintering characteristics of the Fe-C binary mixed powder compacts containing up to 3.0 wt%C were investigated by the dilatometric method. Three kinds of Fe-1.0 wt%C binary mixed powder compacts; each containing electrolytic, atomized and reduced iron powder with different H2 loss, were used in order to examine the process of the carbon diffusion into iron and the decarburization, by means of the dilatometric method, measurement of the degree of vacuum and the carbon analysis.The results obtained are summarized as follows:(1) After the α→γ transformation during heating in vacuum of 10−5 mmHg for the Fe-C binary mixed powder compacts, the expansion was observed, the amount of which was nearly in proportion to the amount of additional graphite, and the expansion curve in dilatation and the combined carbon concentration curve well agreed. This means that the carburization was done mainly by the carbon diffusion through the contacting surface of graphite and iron powder rather than through the medium CH4 or CO gas.(2) From the vacuum measurement, it was apparent that the amount of gas discharge from the specimen with the reduced iron powder was by far larger than that from the other specimens. On the contrary, its dilatational expansion was minimum, indicating that the specimen was not swelled by the gas pressure.(3) Carbon diffusion into α-Fe was scarcely observed in H2 gas sintering, while in vacuum sintering carbon diffusion into α-Fe was about 0.1 wt%. However, the carbon diffused into γ-Fe more rapidly in H2 sintering than in vacuum. Consequently the dilatational expansion in the former was larger than in the latter. A similar relationship between the dilatational expansion curve and the curve of carbon concentration in vacuum sintering was also applicable to the case of sintering in H2 gas.

THE VARIATION OF COEFFICIENT OF FRICTION WITH TEMPERATURE AND COMPACTION VARIABLES FOR IRON POWDER STEARATE-LUBRICATED SYSTEMS

AbstractThe ‘pin and disc’ method has been used to measure the coefficient of friction for the following lubricants: aluminium, calcium, lithium, zinc stearates, and stearic acid. The variation of the coefficient of friction at the surface of iron compacts has been studied with respect to metal/metal contacts exposed through the lubricant film and the behaviour of the lubricant film with variations of pressures, temperature, and speed of sliding has been related to the variation in coefficient of friction for the system.The results for a range of zinc stearates are compared with those for other stearates for reduced iron powder compacts sliding against high-chromium die-steel.

Some properties of reduced iron powder manufactured from Mill-scale

Some key data are presented on the properties of iron powder reduced with a solid reducing agent from low-carbon steel mill-scale and on the mechanical characteristics of specimens pressed from this powder and sintered in hydrogen and dissociated ammonia atmospheres. The properties of iron powder manufactured by the process described meet the requirements of powder metallurgy.

Iron Powder from Iron Oxide Produced by Waste Pickling Liquor Treatment

Iron powders were made from iron oxides by the method of reduction with coke and subsequently with hydrogen. These iron oxides were obtained as a by-product from waste pickling liquor in steel industry. Various properties of these iron powders were tested and measured. The characteristics obtained were as follows:1) Iron powders made from fine oxide particles had low apparent density and irregular shapes compared with those from ore and mill-scale.2) Compressibility was not so good, but compactibility was excellent. Mechanical strength of green compacts was very high, and the rattler value was very small.3) The mechanical strength of these sintered compacts was high in comparison with commercial reduced iron powders and the elongation was especially high at high sintered density.4) The lower is the hydrogen loss of iron powders, the higher both green and sintered densities were obtained then dimensional change (shrinkage) was small and the elongation was much improved.It was found that these iron powders produced by reduction of iron oxides, which were made as a byproduct from waste pickling liquor, had many interesting properties, especially in compactibility and mechanical strength of both green and sintered compacts.

FRICTION COEFFICIENTS BETWEEN IRON POWDER COMPACTS AND DIE WALL DURING EJECTION USING VARIOUS ADMIXED ZINC STEARATE LUBRICANTS

Laboratory compaction and ejection studies have been made using a reduced iron powder mixed with a number of zinc stearates having median particle sizes between 4 and 22μm. Comparable experiments were carried out on a fully instrumented production press, which was operated at compacting pressures between 300 and 500 MN/m2 to produce compacts with true densities ranging from 5·90 to 6·70 g/cm3. Determination of ejection forces by the two methods enabled calculations of the coefficients of friction between compact and die wall to be made for mixtures containing 0·5–2·0 wt.% zinc stearate. These showed that the behaviour during compaction and ejection was comparable on both laboratory and production scales and gave very similar results. An interpretation of the results is given and values of coefficients of friction are presented which show that these are dependent on the type of zinc stearate used.

On the Expansion fo Fe-Cr3C2 Compacts During Sintering

In order to investigate the expansion of Fe-Cr3C2 compacts during sintering, the dilatometric analysis and microscopic examination were systematically carried out by using Fe-Cr3C2 mixed powder compacts which contain up to 30 wt % Cr3C2.The results were summarized as follows:(1) An abnormal expansion appeared in the temperature range between 1050° and 1250°C, and the expansion increased with the increase of Cr3C2 content in the compacts up to 10 wt % Cr3C2, but at higher contents decreased with the increase of Cr3C2 content.(2) This expansion appeared not only in the compacts prepared with reduced iron powders, but also in those of electrolytic, pulverizied electrolytic and carbonyl iron powders, although some difference were observed between them.(3) The expansion observed in the Fe-Cr3C2 compacts did not appear in Fe-Cr, Cr-C, Fe-C and Fe-Cr-C mixed powder compacts, but in the 8.7 Cr-1.3C-Fe mixed powder compacts which corresponding to 10 wt % Cr3C2-Fe there appeared at high temperature.(4) Changes in dimensions of specimens under elevated temperature could be well accounted for from their change in the microstructures.

Effects of Pore-Structure of Sintered Iron Skeletons and Alloying Reaction Between Infiltrants and Skeletons on Infiltrating Phenomena

The present report is concerned with experiments on the infiltrating phenomena of silver, copper and 10%tin-bronze infiltrants into sintered iron skeletons made of three types of iron powders ; that is, (A) electrolytic iron powder made by crashing the electrolytic iron plates, (B) ore reduced iron powder made by crashing the carbon-reduced magnetite ore, (C) mill-scale reduced iron powder made by crashing the carbon-reduced mill-scale of rimmed steel. The results of the experiment can be summarized as follows :1) In the case of silver, which shows no alloying reaction with iron :a) With the complexity of the forms of the iron powders, the pore structures of the skeletons increases in complexity, and consequently the liquid silver decreases in infiltrativity. Infiltration can be performed by using, in the decreasing order of the degree of infiltrativity, (A), (C) and (B) powders.b) The process of infiltrating liquid silver into the skeletons can generally be divided into the following two stages : that is, first the liquid spreads over the surface of the skeleton, and then penetrates into the skeleton. This tendency is most marked when (A) is used. However, the low compactibility of this powder is liable to cause hair cracks in the surface layer of the skeleton.c) Adding a small amount of tin, which shows alloying reaction with both iron and silver, to the iron skeletons, fairly increases the infiltrativity of silver into the skeleton.2) In the cases of copper and 10%tin-bronze, which show mutual alloying reaction with iron, their infiltrativity is very high. However, insufficiency in the volume of the liquid in relation to the porosity of the skeleton is liable to cause the liquid to prefer to penetrate into finer pores of the skeleton, leaving pores unpenetrated.

Antifriction properties of sintered piston rings

1. High antifriction properties of sintered materials for piston rings can be attained by ensuring that their structure is heterogeneous. Such a structure can be achieved in two ways: a) by introducing into the structure of the material soft constituents acting as dry lubricant (graphite and zinc sulfide); b) by establishing in the structure of the material hard, uniformly distributed inclusions having a low coefficient of friction (cementite). 2. Structures of materials with soft or hard inclusions can be formulated by introducing powders of suitable components into the starting charge. To obtain materials with cementite inclusions, it is recommended that chilled cast-iron powder be added to the charge. 3. Sulfides decrease, and cast-iron powder increases, the strength of sintered materials. 4. Material MPK-11 may be recommended as the best for the manufacture of sintered piston rings. The material contains 82.65% of reduced iron powder, 2% of electrolytic copper powder, 1.35% of silvery flake graphite, 4% of zinc sulfide, and 10% of chilled cast-iron powder.

On the preparation of High Density Iron Powder by Reduction of Iron Oxide and Improvement of its Properties

The authors reported previously the sponge iron powder for powder metallurgy which was prepared from pyrite by means of a sequence of the following operations: flotation, roasting and treating with nitric acid, reduction of the purified pyrite cinder with hydrogen, and rolling and annealing of the reduced iron powder.Furthermore, an attempt was made to cut the cost by employing H2-Co gas mixture as a reducing agent. And the authors has succeeded in improving the apparent density and the compressibility of the reduced iron powder by repeating the processes of powder rolling, grinding and annealling.Consequently, they obtained the reduced iron powder having little carbon content and other impurites. The result showed that repeated powder rolling and annealling were effective for densification, and that it was preferable to anneal the powder at a comparatively lower temperature for the improvement of compressibility.Iron powder obtained had compressibility as high as electrolytic iron powder, and the other properties were also satisfactory.

アミン類を主剤とする防食剤の研究 (第32報)

Assuming that chemisorption plays a principal role in inhibition of high molecular-weight amine-type corrosion inhibitors, they firstly act as dehydrater pulling off water which is strongly adsorbed on metal surface, and secondly, occupy the spots produced by departure of the adsorbed water and form inhibitor film on the surface to prevent corrosion. Since functional atoms of polar group of these inhibitors can easily donate unshared electron pairs to hydrogen atoms of the adsorbed water, they can displace the water from the surface by hydrogen-bonding.They can then be adsorbed by donating unshared electron-pairs to the electron-poor metal surface which resulted from the desorption of water. This study was undertaken to discuss relation between the desorption of water and the chemisorption of inhibitors. Reduced iron powder was previously filmed with N, N-dimethyl cetyl amine as an inhibitor in its carbon tetrachloride solution and then the filmed powder was dipped in uninhibited aq. solution of HCl. Inhibition efficiency was obtained by volume measurement of hydrogen evolved from the powder. During the filming, amount of water which was removed from iron powder and remained in the solution was determined by infrared spectrum measurement.It was found that the amount of removed water was very closely related to the inhibition efficiency of the inhibitor-film on the surface of iron powder. The removed water can hardly be re-adsorbed on the metal surface as it is attracted by the inhibitor or other removed water in the solution. Amine inhibitors act as the effective filming agents and also as the effective dehydraters and result in good inhibition for metallic corrosion.

High-Nickel Maraging Steel by Powder Metallurgy (Part II)

The effects of nickel, cobalt and molybdenum on the characteristics of sintering and also on the age-hardenability of sintered maraging steels were investigated. Specimens were prepared by mixing reduced iron powder with alloying element powders, and then compacted at 6t/cm2 and sintered for 1-3 hrs at 1300°C in hydrogen. Subsequently, the sintered compacts were aged for 5 hrs at 500°C. The results obtained are summarized as follows ;1) The densification during sintering was slightly accelerated with the increase of nickel or cobalt content, but it was restrained with molybdenum content.2) Up to a critical amount of alloying elements the aged hardness of compacts steadily increased. When these elements were added in excess, however, there was retained austenite in the martensitic structure of sintered compact, while the aged hardness decreased considerably.It was, therefore, confirmed that the optimum base composition for the maraging steel sintered at 1300°C was of 18% nickel, 7% cobalt and 5% molybdenum.3) Line analysis data by X-ray microanalyzer for Fe-18 Ni-7Co-5Mo compact (sintering: 1300°C× 3hrs) showed that the variations of the average concentrations were ±2% for nickel, ±3% for cobalt and ±0.5% for molybdenum.4) The mechanical properties of sintered compacts are given in table 1, where it is observed that the sintering time and alloy composition have marked effects on mechanical strength, and that sintering at a temperature of 1300°C for the economical time of 1hr gives fairly good results.

High-Nickel Maraging Steel by Powder Metallurgy (Part I)

The investigations on the characteristics of sintering and the age-hardenability of sinte red maraging steels, were carried out. Specimens were prepared from the mixed powder of Fe-18% Ni-7% Co-5% Mo and the atomized alloy powder, followed by compacting under 4-8t/cm2 and sintering or 0.5-5hrs. at 1150-1300°C in hydrogen. The results obtained are summarized as follows.1) After air cooling from the sintering temperature, the sintered compact was relatively soft (<100HR B) with low carbon martensitic structure, which made it amenable to sizing. Subsequent age-hardening given to it for 5hrs. at 500°C, increased its hardness (>30HR c) with negligible contraction.2) For compacts made from the mixed powder, the increase in compacting pressure and sintering temperature or in time was effective in raising the aged hardness, which might be due to the homogenization of alloying elements and the densification during sintering. Under identical conditions of compacting and sintering, the aged hardness of sintered com-pacts produced by mixing the reduced iron powder was, on the average, 2-4 HR c higher than that of electrolytic iron powder.3) Coining and normalizing attempted in advance to age-treatment were not effective for the increase of the age-hardenability of compacts.4) With atomized alloy powder, it was difficult to obtain the densities of more than 7.1g/c.c., even when it was repressed at 4-8t/cm2 and resintered for 1hr. at 1300°C. This may be ascribed to the relatively low aged hardness.

The physics and chemistry of a self-sustained reaction between iron and potassium permanganate

Self-sustained reaction between reduced iron powder and finely powdered potassium permanganate in the proportions 80/20 by weight has been investigated by recording temperature changes as the reaction front passes a point. Velocities of propagation calculated from these records by means of the thermal theory agree well with directly observed velocities. It is therefore considered that this theory is a good representation of the behaviour of this composition, and that it may be used to calculate reaction rates from temperature records. Reaction rates so obtained have been expressed as functions of the absolute temperature and the extent of reaction. It is found that the kinetics at low density (loose powder) are very different from those at high density (hard pellets); and that the difference can be explained on the hypothesis that at low density the reaction takes place by way of the gas phase, and at high density, where contact is better, by diffusion across solid-solid interfaces. It is thought that the mobile species at low density is O 2 , at high density Fe2 + . Support for this view is obtained by measuring the cooling curves of the products and by calculating the atomic heats of the products from observed final temperatures and heats of reaction. Thermal and X-ray data are used in an attempt to formulate the chemical change. In the experimental section, methods of measuring temperatures, thermal conductivities (three methods) and heats of reaction are described.

Magnetic Measurements on Iron Powders

Measured results are given for the permeability and magnetic loss coefficients of carbonyl and hydrogen reduced iron powders, at frequencies from 200 c/s to 40 Mc/s. A method is described for testing cylindrical cores without air-gaps in the magnetic circuit.